1. Technical Field
The present invention relates to ambient environment determination apparatus to determine an ambient environment of a vehicle, in particular, whether the ambient environment is an urban area or a non-urban area.
2. Related Art
When a high beam of a headlight of a vehicle irradiated to a preceding vehicle and an oncoming vehicle, the drivers of the preceding and oncoming vehicles are dazzled by the high beam, which may disturb the drivers in their driving. In order to prevent this, so-called Auto High Beam (AHB) and Adaptive Driving Beam (ADB) are known as light distribution control of the headlight. In performing this light distribution control of the headlight, it is required to recognize the preceding vehicle and the oncoming vehicle existing ahead of the vehicle and recognize whether or not an ambient environment is a running scene in which the high beam of the headlight is acceptable.
A criteria for determining whether or not the high beam may be used in the running scene is whether or not the ambient environment is the urban area or the non-urban area. For example, the AHB by which the high beam is automatically turned on and off regards the high beam as unrequired in the urban area (a scene in which it is sufficiently bright around the neighborhood) and prevents glaring on drivers of vehicles in the neighborhood.
According to a technique described in Japanese Unexamined Patent Application Publication (JP-A) No. 2009-61812, a camera detects a street lamp. When the number of street lamps detected within a certain time exceeds a certain number, and when a time in which the street lamp is detected within a certain period exceeds a certain time, the ambient environment is determined to be an urban area, hence a high-beam nonrequired scene.
In this case, when running environment such as the urban area and the non-urban area is changed, it is preferable to make a determination as quickly as possible to thereby perform accurate light distribution control of the headlight quickly.
On the other hand, in a case where responsiveness of determining whether the running environment is the urban area or the non-urban area is set to be too quick, when temporarily passing through an area where many street lamps and the like are installed in the non-urban area and when entering a situation in which the street lamp cannot be temporarily detected in the urban area, a determination result may fluctuate needlessly, which is not appropriate.